The Principles and Practice of Surveying Volume 1; Elementary Surveying (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1908 Excerpt: ...determined by the instrument at B the backsight on T. P., is too large by the amount cd. Hence the H. I. of the instrument at B is too great, and consequently Report for 1897, pp. 315-320 and pp. 480-489. Report for 1853, pp. 94-96. Fig. 95. Leveling Across A River. the elevation of T. P.2 too great by the amount cd. The mean of the two determinations would give the true elevation of T. P. if ab = cd, but this occurs only when the two sights are taken under the same atmospheric conditions. Therefore it will be seen that the two sights must be taken simultaneously. In order to eliminate the errors of adjustment in the instrument it is necessary to use the same instrument at both ends of the line. To accomplish both of these results at once it is necessary to take simultaneous readings with two instruments and then to repeat the operation with the instruments interchanged. The magnifying powers of the two telescopes and the sensitiveness of the two spirit levels should be about equal in order to give the best results. It will be noticed that this process is similar to that of the peg adjustment (Art. 128, p. 91). Errors due to non-adjustment are of unusual importance because the sight is much longer than that used in adjusting the instrument. 2. Compute the elevations in the following set of level notes. 3. Compute the elevations in the following set of level notes. 4. Make up a set of cross-section notes for road construction which shall be consistent with the following data: width of road, 50 ft., slopes to 1; grade elevation of Sta. o = 107.20; grade, + 1.4. Show complete notes from Sta. o to Sta. 3 inclusive as follows: Sta. o, a level section; Sta. 1, a three level section; Sta. 2, a five level section; Sta. 3, an irregular section. CHAPTER IX. CITY SURV...